1. Field of the Invention
The present invention relates to a composite lens system and a lens unit provided with such composite lens system, as well as an image pickup device provided with such lens unit, and more particularly, to a composite lens system comprising a plurality of lenses which are disposed adjacent one another in a direction of their optical axes aligned with one another by an axis-aligning adjustment.
2. Description of the Related Art
A lens unit 4 including a plurality of (two in FIG. 1) lenses 1 and 2 and another optical part such as a diaphragm within a mirror tube 3, as shown in FIG. 1, has been conventionally used in an image pickup device such as an image pickup camera.
To assemble the lens unit 4 of this type, a process for press-fitting the optical parts 1 and 2 sequentially into the mirror tube 3, beginning with the optical lens 1 which is to be located deeper in the mirror tube 3, as shown in FIG. 1, is conventionally employed in some cases.
When such a process is employed, however, during press-fitting of the first optical part 1 into the mirror tube 3, a sidewall of the mirror tube 3 may be widened, and as a result, the inside diameter of the mirror tube 3 may be slightly deviated from an original design dimension.
This brings about a disadvantage that the second and subsequent optical parts 2 cannot be press-fitted into predetermined locations in the mirror tube 3 and as a result, the positional relationship between the optical parts 1 and 2 is unbalanced, thereby causing the degradation of the optical characteristics of the lens unit 4.
An engagement portion for a body of an image pickup device such as a threaded portion may be formed on an outer peripheral surface of the mirror tube 3. However, when the sidewall of the mirror tube 3 is widened by the press-fitting of the optical part 1 as described above, the outside diameter of the mirror tube 3 may be deviated from an original design dimension, whereby the size of the engagement portion may be also deviated. This causes a disadvantage that the lens unit 4 cannot be engaged appropriately with the body of the image pickup device and thus, is not available as a product.
Therefore, if a plurality of lenses are accommodated in the form of a composite lens system comprising an integral combination these lenses and as required, another optical part, instead of the lenses 1 and 2 being accommodated individually into the mirror tube 3, the above-described disadvantage can be avoided effectively.
However, if the optical parts are merely bonded together, an optical error such as a misalignment between the optical exes of the optical parts may be produced. Therefore, if the optical parts are disposed in an arrangement in which such an error can be eliminated, it is possible to form a composite lens system in which even if the performances of the individual lenses are different from each other, the error can be absorbed to exhibit an appropriate optical performance.
From such a background, various proportions have been made for a lens system in which optical axes of lenses are aligned with each other or with another optical part such as a diaphragm or with a center axis of a mirror tube by an axis-aligning adjustment.
However, the prior art is accompanied by a problem that the axis-aligning adjustment for the optical parts cannot be conducted at a stage of fabrication of a composite lens system, a lot of labor are required for the axis-aligning adjustment and thus, it is impossible to enhance the productivity of a product.
In a case of a lens system in which tapered portions of lenses are brought into abutment against each other for an axis-aligning adjustment, for example, as in a lens system described in Japanese Patent Application Laid-open No.2002-196211, each of the lenses must be formed at an extremely high dimensional accuracy and hence, it is difficult to manufacture the lens system and it is impossible to enhance the productivity.
In a case of a lens system in which a plurality of optical parts are press-fitted sequentially into a mirror tube for an axis-aligning adjustment for the optical parts, as in a lens system described in Japanese Patent Application Laid-open No.2002-286987, it is necessary to determine sizes of the mirror tube and the optical parts at a high accuracy, so that an appropriate press-fitting margin is ensured, on the assumption that the mirror tube is deformed by the press-fitting of the lenses, as described above. For this reason, it is likewise difficult to manufacture the lens system and it is impossible to enhance the productivity.
Further, a lens system described in Japanese Patent Application Laid-open No.2001-344806 is a light pickup lens system and is different in basic arrangement from a lens for an image pickup device. Moreover, in this lens system, an axis-aligning adjustment for lenses cannot be achieved, if they are not in a unit state. Further, the positioning of the lenses in directions of optical axes cannot be conducted univocally and hence, the axis-aligning adjustment is rather complicated.
Yet further, in a case of a lens system in which an axis-aligning adjustment for lenses is conducted after press-fitting of the lenses into a mirror tube, the examination of the optical performance can be conducted only at the time of completion of the assembling of the lenses. As a result, the yield cannot be enhanced, and it is difficult to examine the cause of a failure of assembling and hence, it is further difficult to enhance the productivity.
It is an actual circumstance that there are no effective proposals conventionally made for composite lens systems in which the productivity has been enhanced, while maintaining an optical performance high.